Beverage dispensers for juice, particularly for orange juice, are required to pump a high viscosity juice concentrate and accurately control the ratio of juice concentrate to diluent to produce a beverage of uniform standard. Such dispensers commonly comprise a diluent inlet line from a pressurised diluent source, a juice concentrate reservoir and means for delivering concentrate from the reservoir to the dispenser, which delivering means customarily comprises one of means for pressurising the concentrate reservoir and controlling the flow of concentrate through a valve, means for pumping concentrate from the reservoir and controlling the flow through a valve, or means for volumetrically pumping concentrate from the reservoir. It is known that there are advantages to having a juice concentrate delivery system in which those parts of the system that contact the concentrate are disposable in order to maintain sanitation and reducing the risk of contamination through substandard cleaning of the system.
To improve sanitation in the delivery of juice concentrate from a concentrate reservoir to a juice dispenser the art contemplates use of a rotary peristaltic pump to deliver the concentrate, a deformable tube of which pump forms an integral part of a disposable concentrate reservoir, and use of a positive displacement pump that includes a disposable piston-type pump portion supplied with the concentrate reservoir and a non-disposable drive for reciprocating the pump to draw fluid into and expel it from the disposable pump, as shown in U.S. Pat. Nos. 5,114,047 and 5,154,319.
Peristaltic pumps provide a reasonable solution for sanitation problems, but often experience problems pumping higher viscosity fluids such as juice concentrate, and as the viscosity of juice concentrate can be highly dependant on its temperature, peristaltic systems often do not dispense a correct ratio of juice concentrate to diluent at lower temperatures. In addition, the tube part of the pump often deforms to a permanent set over time, such that the volumetric output towards the end of its life is less than that at the beginning of its life, again affecting the ratio of the mix of concentrate to diluent
Positive displacement pumps, such as that in U.S. Pat. No. 5,114,047, produce a more constant ratio of the mix of juice concentrate to diluent, but because they have a fill cycle and a dispense cycle, the beverage will have a stratified appearance as it exits the dispenser as a result of the concentrate being intermittently dispensed into the diluent stream.
In medical applications dispensers are often required to dispense medical fluids, for example medications, either at their stored concentration or at a lower concentration. These medical applications exist both at patient care level, i.e. administration of medications directly to patients, for example intravenously, and in other areas, for example in dispensaries. With patients contracting such infections as MRSA whilst in hospital it is important that a high level of cleanliness is maintained in medical equipment and drug administration. Many current medical pumps use a disposable reservoir of fluid and a non disposable pump, the pump being required to be cleaned thoroughly between uses, or before every use in infrequently used equipment This cleaning of the pumps needs a human operation to ensure they are adequately cleaned and such human operation introduces the risk of errors and incomplete cleaning.